Originally Posted By: gfh77665
Originally Posted By: OVERKILL
Originally Posted By: gfh77665
The "w" stands for winter, and multi-visc oils try to stay THIN as the temps drop. Where (what temp) is that point where that effect happens? That is what am referring to.
No.
While the "W" designation does denote Winter, it doesn't mean the oil "gets thin".
What it means is simply that the oil RESISTS thickening more than a straight-weight oil like SAE 30 for example.
OK then! "At what temp does the oil RESISTS thickening more than a straight-weight oil"? Can anyone tell me?
Yes, I understand the viscosity principles quite well. I am sorry a seemingly simple question has become SO complex due to semantics.
I guess a simple C or F degree answer was asking too much...
It isn't "a temperature". Not to be rude, but you obviously DON'T understand the viscosity principles quite well, otherwise, the 2nd part of my post, which you omitted from your quote, would have been all you needed to know:
Originally Posted By: OVERKILL
The CCS and MRV values were posted earlier, and they are what define the "W" rating. The lower the MRV and CCS numbers, the less steep the viscosity slope going from cold to hot; the less change there is between the (thicker) cold viscosity and the oil's hot viscosity.
On top of that, there is VI, which is the viscosity index, which gives you the curve/slope for the oil's viscosity between 40C and 100C. This can be extrapolated in either direction, however it doesn't give you accurate information below 0C. This is where MRV and CCS are valuable.
The correlation between viscosity and temperature isn't linear for either a straight-weight oil multigrade oil. What this means is that you can't just assign a number and say "at this point it resists thickening more!". Because that's not how it works. Your initial question was "where does the W effect happen", well, if we were to generalize, we could state that it happens EVERYWHERE, in the ENTIRE viscosity curve. If you compare an SAE 30 lubricant to a 5w-30, from 100C down, if they had the same viscosity @100C, below 100C the 5w-30 would thicken less. When the SAE 30 is jello, the 5w-30 would still be fluid.
However, this is too simple an answer. We've had 0w-30's that are heavier @40C than a 5w-30. So you can't say that the "W effect" starts at 100C then in this case, as both are "winter" rated lubricants and the one that we would assume should be thinner below 100C isn't. This is because the 5w-30 in this case had a higher VI.
BUT, keep dropping the temperature and the curves cross. The 0w-30 eventually thickens less as the temperature plummets and remains fluid longer than the 5w-30.
This is also how you can have an oil like Mobil 1 0w-40 that is THINNER at extremely cold temperatures than a 5w-30, despite being a heavier oil for almost the entire viscosity curve. This is not to say of course that it is thin at -40C, simply that it is thinner than a 5w-30.
